"Here is a fact rarely, if ever, mentioned: 26 of the 50 states set their all-time high temperature records during the 1930s that still stand (some have since been tied)."

"And an additional 11 state all-time high temperature records were set before 1930 and only two states have all-time record high temperatures that were set in the 21st century (South Dakota and South Carolina). So 37 of the 50 states have an all-time high temperature record not exceeded for more than 75 years. Given these numbers and the decreased frequency of days of 100 degrees or higher, it cannot be said that either the frequency or magnitude of heat waves are more common today."

From "Throwing cold water on extreme heat hype" by Dr. Joel N. Myers, AccuWeather Founder and CEO (at AccuWeather).